The present invention is directed to a bicycle power supply and, more particularly, to a bicycle power supply for providing electrical equipment mounted on a bicycle with a voltage produced by an AC generator mounted on the bicycle.
In conventional practice, headlights, taillights, and other types of illumination gear are commonly used as bicycle electrical equipment. Usually, dynamos (AC generators) are mounted on the bicycle to serve as the power supply for such electrical equipment. Currently, however, bicycles are being outfitted with more advanced electrical equipment such as electronically controlled shifters and other mechanisms, and power supplies are needed for the motors, control devices, and other types of electrical equipment used in such equipment. Thus, the power requirements of modern bicycles are becoming quite large.
Not surprisingly, it has been proposed to provide the electric power needed to operate all of the electrical equipment using a dynamo. However, the voltage generated by such a dynamo is an AC voltage, whereas the voltage needed for the electrical equipment is typically a DC voltage. It is therefore necessary to convert the AC voltage produced by the dynamo to a DC voltage. Furthermore, the maximum voltage produced by a dynamo is commonly low (about 8 V) and varies greatly with the travel speed of the bicycle. Thus, if the AC voltage is rectified with a half-wave rectifier circuit, full-wave rectifier circuit, or other type of rectifier circuit commonly used to rectify a 100-V commercial power supply, at some travel speeds it is impossible to provide the electrical equipment with sufficient voltage. Even when a sufficiently powerful voltage can be supplied, the rectified DC voltage varies with the travel conditions, thus making it impossible to provide electrical equipment with stable electric power. A failure to ensure a stable supply of sufficiently powerful voltage makes it more likely that the electrical equipment will malfunction.
The present invention is directed to a bicycle power supply circuit which provides a sufficiently powerful voltage to accommodate greater power demands of electrical equipment mounted on the bicycle. The present invention also is directed to a power supply which provides a stable voltage.
In one embodiment of the present invention, a bicycle power supply circuit is provided whereby an AC voltage from an AC generator mounted on a bicycle is converted to a DC voltage, and the converted DC voltage is provided to an electrical component on the bicycle. The bicycle power supply circuit includes a first input terminal for connecting to a first AC generator output terminal of the AC generator, a second input terminal for connecting to a second AC generator output terminal of the AC generator, a first output terminal for connecting to the electrical component, and a second output terminal for connecting to the electrical component. A full-wave voltage rectifier circuit converts AC voltage presented at the first and second input terminals into a DC voltage, and a storage device is coupled to the voltage rectifier, wherein the storage device has a positive voltage terminal and a negative voltage terminal. The positive voltage terminal is coupled for providing a positive voltage signal to the first output terminal, and the negative voltage terminal is coupled for providing a negative voltage signal to the second output terminal.
In a more specific embodiment, the voltage rectifier includes a first diode having an anode and a cathode and a second diode having an anode and a cathode. The anode of the first diode and the cathode of the second diode are coupled to the first input terminal. A first storage element has a first terminal coupled to the cathode of the first diode and a second terminal coupled to the second input terminal, and a second storage element has a first terminal coupled to the anode of the second diode and a second terminal coupled to the second input terminal.
With this bicycle power supply, voltage is applied to the full-wave voltage rectifier circuit from the first AC generator output terminal of the AC generator via the first input terminal, and charge is accumulated at maximum voltage in the first storage element during the positive half-periods of the voltage provided by the AC generator. Voltage is also applied to the full-wave voltage rectifier circuit from the second AC generator output terminal of the AC generator via the second input terminal, and charge is accumulated at maximum voltage in the second storage element during negative half-periods. As a result, a voltage +Vc appears at the first output terminal, and a voltage xe2x88x92Vc appears at the second output terminal, where Vc is the voltage of the dynamo appearing across the first and second input terminals. Thus, it is possible to output a voltage that is double the maximum voltage delivered by the AC generator, and sufficiently powerful voltage can be stably fed to electrical equipment even when the bicycle is ridden at a low speed as a result of the first and second storage elements.
In an embodiment of the invention that produces a stable voltage, a bicycle power supply circuit as described above includes a voltage regulator that regulates the voltage across the first and second output terminals at a prescribed value. This may be used also in power supplies that do not provide positive and negative voltages at the output terminals. In one embodiment of such a voltage regulator, a switch is disposed between the first input terminal and a storage device, and a switch control circuit is coupled to the switch, to the first output terminal and to the second output terminal. The switch is adapted to sense a voltage across the first and second output terminals and to selectively switch the switch to an off state. This, in turn, keeps the voltage at the first and second output terminals at the desired value.
In another embodiment of a voltage regulator, a switch is provided for switching off a signal at at least one of the first output terminal and the second output terminal, and a switch control circuit is coupled to the switch, to the first output terminal and to the second output terminal. The switch control circuit is adapted to sense a voltage across the first and second output terminals and to selectively switch the switch to an off state when a voltage across the first and second output terminals is less than a prescribed value. Thus, the voltage regulator shuts off the power supply when the voltage falls below a prescribed value to avoid potentially damaging the electronic components. Also, the power shutoff can reduce the charging time needed to return the voltage at the first and second output terminals to the desired value.
If desired, the storage elements may be capacitances, such as large-value capacitors that allow the charging time to be shortened and dimensions reduced. Alternatively, the storage elements may be rechargeable batteries that have a larger storage capacity than capacitors which, in turn, allow for a longer discharge time.
Another inventive feature is the provision of the power supply circuit in a case member that simulates a commercially available battery case. Such a case can simulate a single commercially available battery or a group of commercially available batteries mounted in a commercially available battery case. In this manner a power supply according to the present invention may be inserted in place of a conventional battery, or a conventional battery may be inserted in place of the power supply in the event the power supply needs servicing or when the rolling resistance caused by the dynamo is undesirable in a particular situation.